Is a variable of any valid character data type. @local_variable must be char or varchar, or it must be able to be implicitly converted to those data types.

string_expr

Is an expression that returns a string. Can include concatenated literal values, functions, and variables. The message string can be up to 8,000 characters long; any characters after 8,000 are truncated. For more information, see Expressions (Transact-SQL).